If she claims you on her tax return and you e-filed your tax return first and it is accepted by the IRS, then her e-filed tax return will be rejected by the IRS.
She then can only print and mail her tax return to the IRS. If she leaves you as a dependent on her tax return and has a tax refund the IRS will pay the tax refund.
Within a year both you and her will receive a letter in the mail from the IRS asking that her tax return be amended to remove the dependent on her tax return or you to amend your return and change your dependency. If neither of you amend your tax returns, then the IRS will send another letter requiring you and her to prove either you were or were not a dependent. The loser of the investigation gets to repay any refund based on the dependency plus penalties and interest.
